Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)

Department / School

Animal Science

First Advisor

A. L. Slyter


Sheep are seasonal breeders exhibiting estrus in the fall with the decreasing daylength. This characteristic limits the reproductive performance of the ewe. With the decreasing daylength, melatonin is produced by the pineal gland. This hormone is thought to trigger the onset of estral activity. The study herein attempted to alter this seasonal fertility pattern by subjecting ewes to artificial photoperiod and through the oral administration of melatonin and a melatonin ear implant. The lambs in this experiment were born during late fall which is more favorable than the normal lambing season for the survival rate and growth performance of the lambs. Earlier lambing would also result in lambs being marketed at generally higher prices since these lambs would be sold prior to the influx of lambs from normal seasonal breeding ewes. Hastening the onset of the estrous cycle as was done in this investigation is just one way to increase the reproductive performance of the ewe. The literature review within this thesis will document several other ways the efficiency of reproduction can be increased.

Library of Congress Subject Headings

Ewes -- Reproduction

Sheep -- Reproduction

Ewes -- Breeding

Sheep -- Breeding





Number of Pages



South Dakota State University